The invention relates to a process for the preparation of a hydroxycarboxylic acid via extractive dehydration.
There is much interest in producing various compounds from biorenewable sources. For example, lactic acid, also called 2-hydroxypropionic acid, can be prepared by fermenting sugar, followed by recovering lactic acid from the fermentation broth using distillation or extraction. Distillation methods for recovery of lactic acid from aqueous broth are described in WO 2002/074402. Much has been published regarding use of extractants such as trioctylamines or phosphine oxides to recover hydrophilic carboxylic acids from aqueous solutions. An example is the article by Li, Wang, Li, and Dai, “Extraction of Glyoxylic Acid, Glycolic Acid, Acrylic Acid, and Benzoic Acid with Trialkylphosphine Oxide,” J. Chem. Eng. Data, vol. 48, pp. 621-624 (2003). Conventional methods for extracting acrylic acid from water are described by William Bauer, Jr. in “Kirk-Othmer Encyclopedia of Chemical Technology,” Vol. 1, pp. 342-369 (2003).
Acrylic acid is a very high volume commodity chemical. It can be produced by the oxidation of propylene or propane. However, it would be desirable to be able to economically manufacture acrylic acid from biorenewable resources. Acrylic acid can be prepared from 3-hydroxypropionic acid (3HP). It is known that 3HP can be prepared from renewable resources, such as sugars. Conventional methods call for recovering 3HP from an aqueous solution and then passing the 3HP through a vapor-phase dehydration reactor to convert the 3HP to acrylic acid. However, this requires recovering 3HP directly from aqueous solution, which is difficult and expensive to accomplish, as 3HP, like other hydroxycarboxylic acids such as lactic acid and glycolic acid, is relatively hydrophilic, making it difficult to extract from an aqueous solution or a fermentation broth.
Producing an unsaturated carboxylic acid from biorenewable sources is a complex process requiring multiple unit operations. None of the approaches of the prior art combine chemical dehydration of a hydroxycarboxylic acid compound with simultaneous extraction of the reaction product. It would be desirable to have a simple process for making and recovering acrylic acid and other unsaturated carboxylic acids.